1. Field of the Invention
This invention relates to exterior building wall structures and, more particularly, to composite foam panels with concealed fastening systems. The composite foam panel consists of a structural foam core sandwiched between two metal skins. The metal skins are commonly painted carbon steel, aluminum, or stainless steel of thicknesses ranging from 0.018" (0.46 mm) to 0.048" (1.22 mm). The skins act compositely to resist lateral wind loads by way of shear transfer through the structural foam core. The core is structurally connected to the metal skins by chemical or adhesive bond. The depth of the panel normally ranges from 1 inch (25 mm) to 8 inches (203 mm), depending on load or thermal insulation requirements. The coverwidth of the panel normally ranges from 12 inches (305 mm) to 48 inches (1219 mm). The length of the panel is normally limited to a maximum of 45 feet (13.7 m) due to production, shipping, or field handling limitations. The exterior and the interior metal skins are profiled into separate compatible pairs of male and female side joints. Each panel consists of a fastened side edge and an engaged side edge. Fasteners are used to secure the panel to the building frame along the fastened side edge. The engaged side edge is to cause structural interlocking with the fastened side edge of the adjacent panel, to form a sealed side joint, and to conceal the side joint fasteners of the adjacent panel. In this manner, a number of panel side joints are formed on the finished wall surface without exposing any fastener. Due to the panel length limitation, panel butt joints are formed in most buildings. When the panel side joints are oriented vertically with the panel butt joints running horizontally, the construction is known as vertical panel application. When the panel side joints are oriented horizontally with the panel butt joints running vertically, the construction is known as horizontal panel application.
2. Description of the Prior Art
Composite foam panels have been widely used in exterior wall construction. In designing an exterior wall using composite foam panels, the following four functions must be considered: (1) structural performance against wind loads; (2) thermal insulating performance; (3) weather sealing performance against air and water infiltrations; and (4) fire performance against fire hazards including flame spread and smoke development.
To provide maximum structural strength, it is desirable to have structural interlocking side joints on both the exterior and the interior metal skins. To provide efficient thermal insulating value, it is desirable to minimize the cavities of the wall joints and the panel profile is designed such that the exterior skin is arranged to have no contact with the interior skin to prevent through thermal conductivity. To provide weather sealing, sealing means or means of controlling the running water are provided within the wall joints. In dealing with fire hazard, all building codes specify the maximum limits on two factors known as flame spread and skome development. Recognizing the fact that the metal skins are incombustible while the foam core is combustible, it is easy to understand that limiting the foam core exposure to the air is the key to improve the fire performance. Improving the fire performance is of prime importance in the market place. In case of fire, there are two sources of oxygen supply to the burning foam core. The first source comes from the air flow within the side joint cavity coming in contact with the foam surface exposed within the side joint cavity. The second source comes from air going around the metal side joint after the sealant in the side joint has been consumed in the fire and usually followed by side joint disengagement due to thermal distortions of the metal skins. In an attempt to improve the fire performance, metal clips or straps intermittently connecting the interior and the exterior metal joints together have been utilized. However, this method increases the cost and the thermal insulating performance is compromised due to the through thermal conductivity of the metal clips or straps.
In the weather sealing function, most of the commercially available foam panels are designed to have a male interior joint and a female exterior joint on the fastening side and the corresponding matching male and female joints on the engaging side. This type of profile is found to be unsuitable for horizontal panel application due to the guttering effect of the exterior joint directing the exterior water toward the vertical butt joint causing water infiltration problem. The first method for solving the problem is to eliminate the exterior interlocking side joint. This solution creates three drawbacks, namely, reduced structural strength against negative wind load, unacceptable fire performance against exterior fire, and the necessity of producing separate products for vertical and horizontal panel applications. The second method for solving the problem is explained in my previous U.S. Pat. No. 4,700,520 in which double male joints on the fastening side and double female joints on the engaging side are utilized. The actions of the pulsatory wind loads and the transverse panel deformations produce pulsatory relative movements between the male and the female joints. These pulsatory relative movements of the side joints create a pumping action on the sealant contained in the side joint, therefore, degradation of the sealing performance over time is a rather common occurrence. In the horizontal panel application, the vertical panel butt joint is normally formed by spacing apart the butting panels by a distance of about 1/2 inch (12.7 mm) to 1 inch (25.4 mm). Sealant is applied between the interior panel skin and the mullion surface and a joint gasket is provided across the gap between the exterior skins of the butting panels to act as the rain screen. To prevent the unsightly exposure of the foam core to the exterior viewing along the panel ends, integral end caps extending from the exterior skin are fabricated in the shop. Difficulties would occur when panel length adjustment is necessary in the field due to dimensional tolerance of the building frame. Field fabricated panel end cap is much more inferior in quality to the shop fabricated panel end cap. Due to the degradation of the sealing properties caused by negative wind loads, it is common to experience water leakage problem through the vertical joints within few years after erection. To solve the water leakage problem, water drainage control means such as internal gutter system or intermittent water drainage means explained in my previous U.S. Pat. No. 4,765,107 must be utilized. These solutions incurred additional cost and field workmenship control. In addition, the thermal insulating performance is significantly compromised by the panel gap at the vertical joint such that interior water condensation problem along the vertical mullions may be serious in the cold region.
It is clear from the above review of the prior arts that improving one performance parameter must incur additional cost and/or compromise other performance parameters.